The problems of scale formation and its attendant effects have troubled water systems for years. For instance, scale tends to accumulate on internal walls of various water systems, such as boiler and cooling systems, thereby reducing heat transfer properties and fluid flow through heat exchange tubes.
One particular type of deposit, silica, is especially troublesome in some systems. Where the water used in cooling systems and water-cooled industrial heat exchangers is taken directly from lakes, rivers, ponds or municipal water sources, various amounts of dissolved and suspended solids including silica are present. Problems are compounded in open recirculating water systems due to the fact that as water evaporates the silica concentration increases, thereby increasing both the occurrence and degree of deposition.
In cooling water systems, silica and silicate compounds form deposits on the internal metal surfaces in contact with the water flowing through the system. In this manner, heat transfer efficiency becomes severely impeded, which in turn has a deleterious effect on the overall operating efficiency of the cooling water system. Silica and silicate deposition also causes problems on other conduit and pipe surfaces as well as on equipment such as valves, nozzles and pumps.
Although current industrial cooling systems make use of sophisticated external treatments of the feedwater, e.g., coagulation, filtration, softening of water prior to its being fed into the water system, these operations are only moderately effective. In all cases, external treatment does not in itself provide adequate treatment since muds, sludge, silts and dissolved solids such as silica, escape the treatment, and eventually are introduced into the cooling system.
Various methods have been utilized for resolving the problem of sludge and silt, including silica, deposition. In U.S. Pat. No. 3,578,589, Hwa et al., inhibition of scale, mud, silt and sludge deposition is achieved by adding a nonionic surface active agent, such as a polyethyleneoxy alkyl phenol, and a water soluble polymer, such as polyacrylic acid.
In Watsen et al., U.S. Pat. No. 3,948,792, the patentees disclose the problem of silicate scale formation in automobile and diesel coolant systems. They teach adding a water soluble carboxylic acid polymer and nitrites along with either boric acid or borates.
U.S. Pat. No. 4,869,845, Chen, utilizes the same copolymer as utilized in the present invention to treat scale and corrosion problems in cooling and boiler water systems. The copolymer is added to the system with both a phosphonate and a zinc compound. The purpose of the copolymer is to maintain the solubility of zinc. Without this mechanism, the zinc would precipitate in the form of zinc hydroxide and would be unavailable for its desired anti-corrosion activity.